Electric circuit - denkikairo (English spelling) electric circuit

Japanese: 電気回路 - でんきかいろ（英語表記）electric circuit

Refers to the entire path through which current flows, with circuit elements such as resistors, capacitors, and coils connected to each other. It is also simply called a circuit. When it includes electronic components (electronic devices) such as diodes, transistors, and semiconductor integrated circuits (ICs), it is called an electronic circuit, and there is a distinction between these and other circuits. Elements that do not generate or increase energy, such as resistors, capacitors, coils, and diodes, are called passive elements, while elements that generate or increase energy (strictly speaking, elements that convert energy), such as transistors and vacuum tubes, are called active elements. Hardware that performs the functions of these circuit elements is called a circuit component.

Circuits are called various names depending on their purpose. For example, a circuit that handles direct current is called a DC circuit, a circuit that handles alternating current is called an AC circuit, the circuits that make up a computer are called logic circuits, the circuits that perform calculations within them are called arithmetic circuits, circuits that handle analog signals are called analog circuits, and circuits that handle digital signals are called digital circuits. The academic field that deals with the properties of circuits is called circuit theory. This includes "circuit analysis," which clarifies the response of a circuit to an input, and "circuit synthesis," which clarifies how to create a circuit that exhibits a desired response. To represent circuits, "electrical symbols," which are almost internationally standardized, are used.

[Madashi Fuse and Masazumi Yoshizawa]

Passive and active circuits

A circuit composed only of passive elements is called a passive circuit, while a circuit that includes active elements is called an active circuit. Passive circuits often have a property that their output is proportional to their input. Such circuits are called linear circuits. In contrast, active circuits have a property that their output is not proportional to their input. Such circuits are called nonlinear circuits. Oscillator circuits are a typical example. Amplifier circuits are also nonlinear circuits, but since their output is proportional to their input when the signal strength is weak, they are often treated as approximately linear circuits.

[Madashi Fuse and Masazumi Yoshizawa]

Distributed constant circuit/lumped constant circuit

When the dimensions of a circuit are comparable to or larger than the voltage applied to the circuit, the current flowing through the circuit, or the wavelength of the electromagnetic waves traveling on the circuit, the voltage, current, or electromagnetic waves will interfere with each other and produce standing waves in the circuit. This type of circuit is called a distributed constant circuit. Standing waves in a circuit often cause problems, but they can be used to create a resonator. Examples of distributed constant circuits include antennas and feeders.

Waveguides used in microwaves are also distributed constant circuits, and are called three-dimensional circuits due to their shape. On the other hand, if the dimensions of the circuit are small enough compared to the wavelength, interference from voltage and current can be ignored. Such circuits are called lumped constant circuits. Examples of lumped constant circuits include household electric lights and heaters and their wiring, and the circuits of low-frequency electronic devices.

[Madashi Fuse and Masazumi Yoshizawa]

[Reference] | Linear circuits | Nonlinear circuits | Distributed constant circuits

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

抵抗器、コンデンサー、コイル等の回路素子が互いに接続された電流の流れる通路全体をいう。単に回路ともいう。ダイオード、トランジスタや半導体集積回路（IC）等の電子部品（電子デバイス）を含む場合を電子回路とよび、区別する場合もある。抵抗器、コンデンサー、コイル、ダイオードのようにエネルギーを発生したり増大したりしない素子を受動素子とよび、トランジスタや真空管などのようにエネルギーを発生または増大する素子（厳密にはエネルギーを変換する素子）を能動素子とよぶ。これらの回路素子の機能を果たすハードウェアを回路部品という。

　回路は目的に従っていろいろな呼び方をする。たとえば、直流を扱う回路を直流回路、交流を扱う回路を交流回路、コンピュータを構成する回路を論理回路、そのなかで演算を行う回路を演算回路、アナログ信号を扱う回路をアナログ回路、デジタル信号を扱う回路をデジタル回路などという。回路の性質を取り扱う学問分野を回路理論という。これには、入力に対する回路の応答を明らかにする「回路解析学」と、所要の応答を示す回路の作り方を明らかにする「回路合成学」とがある。回路を表記するには、国際的にほぼ統一された「電気用図記号」を用いる。

［布施　正・吉澤昌純］

受動回路・能動回路

受動素子だけで構成されている回路を受動回路、能動素子を含む回路を能動回路とよぶ。受動回路は多くの場合出力が入力に比例する性質がある。このような回路を線形回路とよぶ。これに対して、能動回路では出力は入力に比例しない性質がある。このような回路を非線形回路とよぶ。発振回路がその典型である。増幅回路も非線形回路であるが、信号の強さが微弱な場合は出力が入力に比例するので、近似的に線形回路として扱うことが多い。

［布施　正・吉澤昌純］

分布定数回路・集中定数回路

回路の寸法がその回路に加わる電圧や、回路を流れる電流、あるいは回路上を伝わる電磁波の波長と同程度以上になると、電圧や電流、または電磁波は干渉をおこして回路に定在波を生ずる。このような回路を分布定数回路という。回路に定在波が生じると多くの場合は障害となるが、定在波を利用して共振器を構成することができる。分布定数回路の例としては、アンテナやフィーダーなどがある。

　また、マイクロ波で用いられる導波管なども分布定数回路であり、その形状から立体回路とよばれる。これに対して、回路の寸法が波長に比べて十分小さい場合は、電圧・電流などの干渉は無視できる。このような回路を集中定数回路という。集中定数回路の例としては、家庭の電灯・電熱器およびその配線や、低周波のエレクトロニクス機器の回路などがある。

［布施　正・吉澤昌純］

[参照項目] | 線形回路 | 非線形回路 | 分布定数回路

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例

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